1. Field of the Invention
This disclosure relates generally to an interventionless actuator for oil well tools and, more particularly, to an interventionless actuator having a floating piston.
2. Description of the Related Art
A typical hydrocarbon well, whether on land or under water, is drilled into the earth's surface to form a well bore. A protective casing may be run into the well bore and the annulus formed between the casing and the well bore filled with a concrete-like mixture. Several types of tools may be run into the cased well bore to complete the well and subsequently produce hydrocarbons from the well. Most of these tools and equipment require that one or more actuating events occur. For example, mechanical actuation can be accomplished by physically pushing, pulling or rotating one or more parts of the down hole equipment. For example, a mechanical well or formation isolation tool may use a shifting tool to open and/or close the isolation element. Such mechanical actuation requires intervention into the well bore and such intervention is often times undesirable. In response, the industry has developed interventionless tool actuators that, as the name implies, do not require mechanical access to the well bore.
In the context of well isolation tools, U.S. Pat. No. 6,662,877 discloses mechanical actuation in the form of a shifting tool that is used to mechanically move a sleeve, which in turn causes the isolation element to transition from closed state to an opened state, and vice versa. This patent also discloses interventionless actuation to open the closed valve element. The interventionless actuator comprises a nitrogen chamber and an indexing mechanism. Repeated pressurization and depressurization of the inside of the tool causes the isolation element to open after a predetermined number of pressure cycles advance the indexing mechanism. To provide the necessary actuation energy, the nitrogen chamber must be charged at the surface to a pressure at least greater than the hydrostatic pressure to be encountered in the well, which may be 8 to 10 kpsi or higher. Such high pressure charging and equipment is potentially dangerous and often times undesirable on the rig floor.
This application for patent discloses an improved interventionless actuator for oil well tools.